Field of Invention
This invention relates to a tire pressure control system (TPCS) having a rotatable air passage. In particular this invention relates to a tire pressure control system for measuring the tire pressure on an agricultural vehicle, or machine having a rotatable air passage.
Description of Related Art
In order to improve efficiency and safety of an agricultural machine, or an agricultural vehicle such as an agricultural tractor, it is necessary to change the pressure of the tires depending on whether the tractor is operating, or on the road. When operating in the field, lower tire pressures are required to reduce ground pressure and compaction and to improve the grip of the tires with the earth. For road work, higher tire pressures are required to reduce rolling resistance (which affects the efficiency of the tractor) and to reduce heat generation (which affects the safety of the tractor). The pressures of the tires may typically be varied by 0.6 bar-2.5 bar when moving between field and road surfaces.
Known tire pressure control systems (TPCS) suffer from the fact that the integrity, that is the air tightness of the tire inflation arrangement, for example the integrity of the tire valves is not monitored sufficiently during operation.
Two methods (described below as method A and method B) are generally known to be used to detect leakages during inflation and deflation of a tire on a vehicle:
Method A. When inflating or deflating the tire, the pressure control system checks the integrity of the arrangement by checking whether the target, or desired tire pressure can be reached within a pre-determined time. If not, a leakage is likely. This has the major disadvantage that in the case of a large tire pressure increase, the TPCS is in operation for a long time because of the lengthy inflation time before the failure is detected.
Method B. Each tire is equipped with a pressure sensor. The sensor is used to monitor the tire pressure permanently or temporarily assuming that a change in tire pressure without actively changing the tire pressure via TPCS indicates a leakage. This may work for the tire itself but leakages in the supply line, especially in the pipes, hoses and rotary passages outside of the tire cannot be monitored. This may again require method A. Furthermore, method B requires pressure sensors in all tires which has cost implications.
The known methods do not offer a monitoring system for a TPCS which can be operated without changing the tire pressure, or which can monitor the integrity of components outside of the tire.